touch to instantiate and move object ?

Touching to spawn objects is not really something you want to happen if you want to be able to move placed objects later on. Here's what I would do personally:

Have buttons that spawn different Game Objects and then keep a reference for them for example:

 public GameObject curObject;
 public LayerMask objLayer;
 if(GUILayout.Button("Spawn Cube"))
 {
     curObject = GameObject.CreativePrimitive(PrimitiveType.Cube);
 }

Touch controls come with phases, which give you access to information similar to events, which you can use as follows:

 void Update()
 {
     //This will get the first touch available when the finger is moving
     if (Input.GetTouch(0).phase == TouchPhase.Moved && curObject != null)
     {
         //This may be incorrect, I don't have Unity in front of me.
         //If this is wrong, look at transforming this to a world co-ordinate.
         curObject.transform.position = Input.GetTouch(0).Position;
     }
     //The finger has left the screen and we have a curObject that we were moving
     if(Input.GetTouch(0).phase == TouchPhase.Ended && curObject != null)
     {
         //Set up a layer specifically for movable GameObjects and set that
         //layer number here, you'll see why in a second
         curObject.Layer = 6;
         //We're done with the current object, so our reference to it must now be
         //removed
         curObject = null;
     }
     //We don't have a current object, time to find one
     if (Input.GetTouch(i).phase == TouchPhase.Began && curObject == null) 
     {
         // Construct a ray from the current touch coordinates
         Ray ray = Camera.main.ScreenPointToRay (Input.GetTouch(i).position);
         RaycastHit hit;
         if (Physics.Raycast (ray, out hit, Mathf.Infinity, objLayer))
         {
             //We've hit something, information is in the RaycastHit object.
             curObject = hit.transform.GameObject;
         }
     }
 }

Things for you to read: Raycast information RaycastHit information Layers and LayerMasks